Motor safety control method and robot for implementing the same
Disclosed herein are a motor safety control method that can efficiently detect an abnormality of a motor sensor configured to sense a rotational motion of a motor and control a safety operation of the motor based thereon, and a robot for implementing the method. The motor safety control method for a robot may include receiving a first motor value from a high-resolution sensor of a motor, receiving a second motor value from a low-resolution sensor of the motor, and comparing a threshold with a difference between the first motor value and the second motor value, and transmitting an operation signal to a motor driver for the motor to continue or stop operation of the motor.
1 . A motor safety control method for a robot, comprising:
receiving a first motor value from a first sensor of a motor;
receiving a second motor value from a second sensor of the motor, wherein a resolution of the first sensor is higher than a resolution of the second sensor;
inputting the first motor value and the second motor value respectively to a first speed sub-monitor of a speed monitor of a safety controller configured to compute a first rotational speed of the motor based on the first motor value and a second speed sub-monitor of a speed monitor of the safety controller configured to compute a second rotational speed of the motor based on the second motor value;
comparing a threshold with a first difference between the first rotational speed and the second rotational speed at the first speed sub-monitor and comparing the threshold with a second difference between the first rotational speed and the second rotational speed at the second speed sub-monitor; and
transmitting an operation signal to a motor driver for the motor to continue or stop operation of the motor based on comparisons at the first speed sub-monitor and the second speed sub-monitor.
2 . The method of claim 1 , wherein:
the first sensor comprises a motor encoder; and
the second sensor comprises at least one Hall sensor disposed inside the motor.
3 . The method of claim 1 wherein the operation signal is one of:
an operation ongoing signal for operation of the motor to continue; or
an operation stop signal for operation of the motor to stop.
4 . The method of claim 3 , wherein the operation ongoing signal is transmitted to the motor driver based on the first difference and the second difference both being within the threshold, and
the operation stop signal is transmitted to the motor driver based on one of the first difference or the second difference being outside of the threshold.
5 . The method of claim 1 , wherein the first motor value is input to the second speed sub-monitor via the first speed sub-monitor, and
wherein the second motor value is input to the first speed sub-monitor via the second speed sub-monitor.
6 . The method of claim 1 , further comprising:
inputting two motor values of another motor to the first speed sub-monitor and the second speed sub-monitor, respectively.
7 . The method of claim 1 , wherein the first speed sub-monitor generates a first operation sub-signal based on the first difference,
wherein the second speed sub-monitor generates a second operation sub-signal based on the second difference, and
wherein the safety controller generates the operation signal based on the first operation sub-signal and the second operation sub-signal and outputs the operation signal to the motor driver.
8 . The method of claim 7 , further comprising:
transmitting the first motor value, the second motor value, the first operation sub-signal, and the second operation sub-signal to a processor of the safety controller.
9 . The method of claim 8 , further comprising:
receiving a target travel speed of the robot from a path guider; and
verifying, by the processor, correctness of the first operation sub-signal and the second operation sub-signal by comparing the target travel speed with the first motor value and the second motor value.
10 . The method of claim 9 , further comprising:
outputting, by the processor, the operation stop signal to the motor driver based on a difference between the target travel speed and a travel speed of the robot according to at least one of the first motor value or the second motor value being out of a predetermined range, even when the first operation sub-signal and the second operation sub-signal correspond to operation ongoing signals.
11 . The method of claim 9 , further comprising:
transmitting, by the processor, a first control signal to the speed monitor for causing the speed monitor to output the operation stop signal to the motor driver based on the difference between the target travel speed and the travel speed of the robot according to at least one of the first motor value or the second motor value being out of a predetermined range.
12 . The method of claim 11 , further comprising:
monitoring, by a power manager, power usage of the processor for abnormalities; and
transmitting, by the power manager, a second control signal to the speed monitor for causing the speed monitor to output the operation stop signal to the motor driver based on abnormal power usage of the processor.
13 . The method of claim 1 , further comprising:
determining, from a traveling safety sensing signal received from a traveling safety sensor, whether there is an obstacle present in a safety zone;
requesting a drive unit to decelerate to a safe speed based on determining that the obstacle is present; and
outputting the operation stop signal to the motor driver based on the motor driver not having decelerated to the safety speed within a predetermined time.
14 . The method of claim 13 , wherein the operation stop signal comprises:
a safety stop (SS) signal for decelerating the robot to a target stop speed in response to detection of an abnormality of at least one of the motor, the first sensor, or the second sensor; and
a safe torque off (STO) signal for blocking generation of torque by the motor after the robot is decelerated to the target stop speed.
15 . A robot comprising:
a motor;
a first sensor configured to sense a first motor value for the motor;
a second sensor configured to sense a second motor value for the motor, wherein a resolution of the first sensor is higher than a resolution of the second sensor;
a motor driver configured to provide a drive signal to the motor;
a safety controller comprising a first speed sub-monitor and a second speed sub-monitor and configured to:
receive the first motor value and the second motor value respectively at the first speed sub-monitor configured to compute a first rotational speed of the motor based on the first motor value and the second speed sub-monitor configured to compute a second rotational speed of the motor based on the second motor value;
compare a threshold with a first difference between the first rotational speed and the second rotational speed at the first speed sub-monitor and comparing the threshold with a second difference between the first rotational speed and the second rotational speed at the second speed sub-monitor; and
provide an operation signal to the motor driver to continue or stop operation of the motor based on the comparisons at the first speed sub-monitor and the second speed sub-monitor.
16 . The robot of claim 15 , wherein:
the first sensor comprises a motor encoder; and
the second sensor comprises at least one Hall sensor disposed inside the motor.
17 . The robot of claim 15 , wherein the operation signal is one of:
an operation ongoing signal for operation of the motor to continue; or
an operation stop signal for operation of the motor to stop.
18 . The robot of claim 17 , wherein, the operation ongoing signal is transmitted to the motor driver based on the first difference and the second difference both being within the threshold,
the operation stop signal is transmitted to the motor driver based on one of the first difference or the second difference being outside of the threshold.
19 . The robot of claim 15 , wherein the safety controller comprises:
a speed monitor configured to generate a first operation sub-signal and a second operation sub-signal based on the first motor value and the second motor value;
a processor configured to verify correctness of the first operation sub-signal and the second operation sub-signal; and
a power manager configured to monitor power usage of the processor for abnormalities,
wherein the safety controller is implemented as a single board and mounted on the robot.